Something
that has continued to evolve over the life of the game has been
end-game progression, and what’s required of your character to see what
is at any one time considered the final raid. Originally it was a very
linear path. You had to gear up through one raid before you could
attempt the next, and the one after that, and so on. It meant that if
you were even slightly behind the curve you could potentially never
catch up. We began adding mechanics and options in Burning Crusade and
beyond to ensure players could, with effort, have some ability to catch
up. Fast forward to Cataclysm where we believe we went too far the other
direction and a freshly minted 90 didn’t really have to do anything
before jumping directly into Dragon Soul.

In Mists of Pandaria we
want to get back to where we were in helping people catch up, but only
through some effort in completing prior content. We don’t want it to be a
linear A->B->C model again, because that causes a lot of undue
burden on guilds attempting to catch up alts and replacements, but we
also don’t want the Cataclysm model of being able to more or less skip
straight to the end, invalidating everyone’s efforts who came before.

New
characters coming into Mists of Pandaria will be going through
Mogu’shan Vaults, Heart of Fear, and Terrace of Endless Spring, killing
bosses, and gearing up before moving on. Due to that we’ll be adjusting
the difficulty, as well as item drops, to make progression a bit quicker
without shortcutting people directly to the Throne of Thunder raid.
With the release of 5.2 enemy health and damage in the three prior raids
will be reduced by 10%. We expect this to be a one-time reduction, and
not a slowly increasing reduction as we’ve done previously. In addition,
item drops are being greatly increased, including those from Elder
Charm of Good Fortune bonus rolls. In addition, as stated in the patch
notes, costs of 5.0 and 5.1 Valor items are being reduced by 50% and 25%
respectively.

IN ADDITION! If you’re killing bosses in Normal
and Heroic before 5.2 releases, and thus pre-nerf, you’ll actually get
Feats of Strength honoring the accomplishments you made before the
change – which is pretty cool. IMO.

With these changes we hope to
see players able to catch when coming into the game mid-expansion, or
leveling an alt, but still putting in the time and effort to get to the
latest tier.

I specifically asked Bashiok on twitter what we would be spending Valor on if they want people to do old raids to gear up for the new raids instead of leap frogging to the new raids bypassing all old content. An he reminded me:

I had totally forgotten all about that. I love this change to be honest. I have wanted valor gear to be moved into raids and require raiding to purchase for a long time.If you don't raid you don't need that gear and you still get item level 502 gear in lfr.